1. Field of the Invention
The present invention relates to an LED driving circuit having an error detection function that is applicable to an LED TV set using an LED backlight unit, and more particularly, to an LED driving circuit having an error detection function that can detect errors caused by noise such as a surge or electrostatic discharge.
2. Description of the Related Art
In general, liquid crystal displays (LCDs) are light receiving elements that cannot emit light by themselves, and thus necessarily require backlight units (BLUs) in order to display a screen.
Cold cathode fluorescent lamps (CCFLs) and external electrode fluorescent lamps (EEFLs) have been used as the light sources of these backlight units (BLUs).
However, recently, a backlight unit has been manufactured using light emitting diodes (LEDs) that are environment friendly, have low power consumption, and have a high contrast ratio and excellent color reproducibility.
A method of driving this backlight unit causes motion blur due to an after image when one screen is converted into another screen, which leads to poor image quality.
In order to solve these problems, local dimming and scan dimming are being used. Here, according to scan dimming, backlight units (BLUs) are sequentially turned on according to image signals being input to the backlight units (BLUs) from top to bottom.
FIG. 1 is a block diagram illustrating an LED backlight unit (BLU) according to an exemplary embodiment of the invention. As shown in FIG. 1, an LED backlight unit includes an LED lamp array 10 having a plurality of LED lamps and an LED driving circuit 20 having a plurality of LED driving ICs driving the LED lamp array 10.
The LED driving circuit 20 performs local dimming and scan dimming by using a vertical synchronization signal Vsync and pixel values included in image data from an image processing block 30 (also known as an image processing board) to thereby generate driving signals as shown in FIG. 2.
FIG. 2 is a timing chart illustrating driving signals obtained through scan dimming of an LED backlight unit. In FIG. 2, for one period of the vertical synchronization signal Vsync, a plurality of driving signals DS0 to DS9 have high levels in a sequential manner. The LED driving ICs sequentially turn on the plurality of LEDs.
Meanwhile, in an existing backlight unit, an image processing block directly generates LED PWM signals in association with scan/local dimming and supplies the LED PWM signals to the LED driving ICs. However, this driving method requires the number of lines to be as many as the number of channels to be driven, which increases the manufacturing costs of a PCB board.
In order to solve these problems, recently, a driving method has been used in which LED driving ICs receive only the data necessary for dimming from an image processing block and directly generate signals in association with dimming.
These LED driving ICs will be described in brief. An LED driving IC generates a PWM signal for local dimming and an LED turn-on time control signal for scanning. In order to generate the PWM signal and the LED turn-on time control signal, the LED driving IC stores a control signal and a specific command therein and periodically generates a PWM signal according to the stored command.
That is, in order to generate a PWM signal and an LED turn-on time control signal in order to perform LED dimming (local and scan dimming), the LED driving IC receives the following three types of data from the image processing block and stores these data in an internal register:
local dimming data (0 to 255) to generate a PWM signal
a scan dimming start point indicating a start point of scan dimming, and
a scan dimming mask indicating a scan dimming turn-on interval.
The LED driving IC can turn on an LED driving PWM signal by using these three types of data.
However, when this LED driving IC is applied to a display device such as a television or a monitor, it is exposed to various noise such as electrostatic discharge (ES) and a surge, which lead to signal distortion and ultimately cause the LED driving IC to malfunction.